The tube could sit on rollers and/or the expansion could go into pushing arcs out slightly more. There are probably a lot of solutions. It doesn't necessarily

The tube could sit on rollers and/or the expansion could go into pushing arcs out slightly more. There are probably a lot of solutions. It doesn't necessarily need to be a perfect vacuum. The less air in the tube, the less resistance there will be. I would guess there would be vacuum pumps constantly taking air out of it.